Integrated circuits are still more and more highly integrated; in the manufacture of semiconductor tips such as VLSI's, processing of ultra-fine patterns comprising line widths below half a micron is required. To satisfy such a requirement, the wavelength of the light used for photolithographic exposure is becoming shorter and shorter. Recently, the use of excimer laser (including XeCl, KrF and ArF) lights that belong to shorter wavelength regions of deep UV light is being investigated.
For the lithographic pattern formation with the lights in such wavelength regions, chemically amplified resists have been proposed.
Generally speaking, chemically amplified resists can be classified into three types, i.e., a so-called two-component system, a two and a half-component system, and a three-component system. The two-component system consists of a compound which photolytically generates an acid (Such a compound will be called a photo acid-generator hereinafter.) and a binder resin. The binder resin contains a group that undergoes decomposition by the action of the acid to increase the solubility of the resin into an alkaline developer. Such a group is sometimes called an acid-decomposable group. The two and a half-component system contains a low molecular weight compound having an acid-decomposable group in addition to such two components. The three-component system comprises a photo acid-generator, an alkali-soluble resin and the low molecular weight compound.
Although the above described chemically amplified resists are suited for the exposure to UV or deep UV light, they must further keep up with various requirements for practical use. As the photoresist composition designed for ArF light sources, those comprising a (meth) acrylic resin that shows a still weaker absorption than partially hydroxylated styrene-based resins for the ArF light combined with a photo acid-generating compound have been proposed.
For example, Japanese Patent Laid-Open Nos. 199467/1995 and 252324/1995 describe such photoresist compositions. In particular, Japanese Patent Laid-Open No. 289615/1994 discloses a resin in which a tertiary carbon-containing organic group is bonded via an ester linkage to the oxygen in the carboxyl group of acrylic acid.
Japanese Patent Laid-Open No. 234511/1995 discloses acid-decomposable resins comprising repeating units of acrylate esters or fumarate esters, but these resins are not yet satisfactorily used due to their insufficient pattern profiles and poor adhesion to substrates.
Separately, there are proposed resins to which an alicyclic hydrocarbon part is introduced for the purpose of imparting the resistance to dry etching.
Japanese Patent Laid-Open Nos. 73173/1997, 90637/1997 and 16131/1998 disclose a resist material comprising an acid-responsive compound having a structural unit in which an alkali-soluble group protected with a group having an alicyclic structure is attacked by an acid to release said alkali-soluble group thus converting the unit soluble in an alkali.
Further, Japanese Patent Laid-Open Nos. 90637/1997, 207069/1998 and 274852/1998 describe resist compositions based on an acid-decomposable resin having a specified lactone structure.
In the lithographic processes for the manufacture of devices using design rules of 0.18 μm and not exceeding 0.13 μm. 193 nm wavelength light is often used to expose resists. Accordingly, resist polymers not abundant in ethylenically unsaturated structure are desired.
Although the resists disclosed in Japanese Patent Laid-Open Nos. 10739/1998 and 307401/1998 have an improved transmittance to 193 nm wavelength light, they do not always exhibit a sufficiently high sensitivity. In the case of applying those resists to the lithography using design rules of 0.13 μm or shorter, the resist characteristics cannot meet practical requirements such as pattern resolution.
In Japanese Patent Laid-Open No. 130340/1998, chemically amplified resists comprising a terpolymer containing a specified norbornene repeating unit in its principal chain.
In Japanese Patent Laid-Open No. 305444/1999, resins are described comprising a repeating unit having an adamantane structure in its side chain together with another repeating unit of maleic anhydride.
However, all of these chemically amplified resists are still unsatisfactory as regards to the resolution for fine contact hole patterns or trench patterns, and also pattern pitch dependency.
A contact hole is provided to lead an electrode metal of a semiconductor device to the semiconductor surface. Recently, in the manufacture of semiconductor devices, not only the pattern line width but also the configuration of the contact hole is becoming finer. Accordingly, positive photoresist compositions which can well resolve very fine contact hole patterns are eagerly desired. Unfortunately, it has not been clarified how to optimally design a resist composition that can resolve extremely fine contact holes. Moreover, it is now being recognized that resists suited for obtaining fine line width patterns are not always suited for resolving extremely fine contact hole patterns.
A trench, which indicates a connected groove pattern, is also becoming finer similarly to contact holes. Hence, positive photoresist compositions that can resolve fine trench patterns are also eagerly desired.
Further, the structure of devices is becoming more and more complicated, and in particular in logic-related devices it is necessary to simultaneously form patterns of various pitches ranging from crowded patterns to isolated ones. Unfortunately, since the conventional resist materials exhibit sensitivities strongly dependent on pattern pitch, desired pattern dimensions have not been reproduced with the same exposure for crowded and isolated patterns. Solution of such an issue, sometimes called pattern pitch dependency, has been earnestly expected.